1. Field of the Invention
The present invention relates to a high frequency heat treatment method for fine bottom-closed holes, and, more particularly, to a high frequency heat treatment method, which enables simplification of process and cost reduction via improvement of a conventional high frequency heat treatment method while ensuring high quality.
2. Description of the Related Art
Generally, sintered components for a part requiring high strength are enhanced in mechanical properties via heat treatment in a post process. In particular, high frequency heat treatment has been widely used to enhance a local property of a component having a large volume due to its merits in that it can ensure stable quality and reduce manufacturing costs in comparison to typical heat treatment.
The high frequency heat treatment is a process by which only a target part of a material is transformed to an austenite structure, and then transformed to a martensite structure via quenching under preset operating conditions such as suitable shape and size of a coil, frequency, output power, and time.
For the case of sintered component, the high frequency heat treatment is generally applied to parts such as an outer periphery, a cross-section and a punctured hole of a component, which have shapes allowing easy manufacture of a high frequency coil, to teeth of a chain gear, which allow easy operation of the high frequency heat treatment, and to parts such as a cross-section or an inner surface of a clutch hub, which require wear resistance and stiffness.
However, for the case of a fine bottom-closed hole such as a pin stopper hole used to determine a location of a rotor for a sprocket module of a variable timing valve applied to a vehicle, since it is manufactured by pressing a brush having a high hardness for wear resistance, there occurs a problem of low operation efficiency due to high frequency of defective products, complicated process, and high manufacturing costs.